Natural regeneration methods for forest tree species

1. LECTURE 4: FOREST REGENERATION –
NATURAL REGENERATION
Dr. B. Sangeetha
Asst. Professor, KITS.

2. Regeneration
The renewal of a forest crops by natural or artificial means also the new crop so obtained.
The renewal by self-sown seed or by vegetative means.
Regeneration Methods
1. Natural regeneration
2. Artificial regeneration
3. Natural regeneration supplemented with artificial regeneration

3. 1. Natural regeneration
Renewal of a forest crop, by seed sowing, germination, establishment
or by coppice or root-suckers, also the crop so obtained or also it can be
defined as Reforestation of a stand by natural seeding.
Example: Predominantly in dry and moist deciduous forest
From seed – ‘High forest’ or ‘seedling crop’. sexual method of regeneration
in which the new plant exhibits the characters of both the parents.
From vegetative parts – Asexual method of regeneration and the new plant
exhibits the characters of the parent plant only. Regeneration is obtained
from coppice, it is called coppice crop, and the latter develops into a forest
called coppice

4. Natural Regeneration through Seed
Natural regeneration from seed goes through the following
four processes, namely
• Seed production
• Seed dispersion
• Seed germination
• Seedling establishment

5. 1.Seed Production
The most important prerequisite of natural regeneration is the production of adequate quantities of
fertile seeds by the trees of the area or immediate neighbourhood. Seed production depends on,
• Species of the tree
• Age of tree
• Crown size
• Apical dominance
• Climatic conditions
• Season of maturity
• Alternate bearing
• Biotic and abiotic factors

6. 1. Seed Production
Seed production depends on,
(a) Species
(b) Age of the tree
(c) Soil conditions
(d) Climate
(e) Crown size
(f) Other external factors.

7. Species
Seed production is primarily a specific character. That is, all species do not seed annually
and in equal abundance. For example, Teak, Sissoo and Acacias seed almost every year,
whereas it is not so for many other species. For some important species, good seed years
occur at Intervals as shown below.
• Sal sp. - 3 years • Terminalia sp.- 2 years • Cedrus deodara - 4-5 years

8. Age of the tree - Best seeds are produced from middle- aged to medium-sized parent trees. Young as
well as very old trees produce seeds with less germinating capacity and reduced vigour.
Soil condition - Seed production is favoured in soil having sufficient bases, adequate nitrates and higher
C/N ratio.
Climate - In general, a warmer climate favours early and heavy seed production
Crown - Large well developed lighted crowns bear more seeds and of bigger size than trees with poor
and ill-lighted crowns

9. Otherexternalfactors- Other external factors which influence seeding are (i) fire injury,
fungus and insect attack and (ii) girdling.

10. 2. Seed dissemination
Seed dissemination or seed dispersal is caused by the following agencies
 Wind – Seeds which are dispersed by the wind are either winged or hairy. Winged seeds are found
in Dipterocarpus, Termenilias, Conifers, Holoptelia, Dalbergia, Acer, Pterocarpus, Adina, Betula,
Rhododendron, and Oroxylon. Hairy seeds are found in Bombax, Populus, Salix, Family Eupetorium
and grasses e.g Saccharum and Imperata.
 Water – Examples of water dispersed seeds are most mangrove species, Teak, Dalbergia, Trewia,
and most of the wind dispersed seed, if they can retain their viability in water.

11.  Gravity – Seeds are dispersed by gravity in case of the following species, namely, Acorns of
Oaks, Juglans regia, Diospyros and other heavy seeded species on sloping ground.
 Animals – Seeds of the following species are dispersed by birds- Prunus, Mulberry,
Loranthus etc. Seed dispersals of following species are caused by animals- Acacia arabica,
Prosopis Juliflora, Ziziphus, Anthocephalus etc.
 Explosive mechanism – Examples are Oroxylon and species of acanthaceae

12. 3. Seed germination
The process that follows seed-fall is the germination of seeds. This process is dependent
upon
(i) Internal factors
(ii) External factors.

13. A. Internal factors - Internal factors are the factors pertaining to the seed itself.
Internal factors affecting germination are
Permeability of water – A hard seed-coat prevents germination through lack of contact of
the seed with moisture.
Permeability to Oxygen- Oxygen is necessary for seed germination. Factors which inhibit
moisture reaching the seed also prevent oxygen reaching it.
Nature of Embryo - The embryo should be fully developed at the time of seed fall,
otherwise the seeds will have to go through a period of dormancy till the embryo is fully
developed.

15. After ripening process - This is the most common cause of delayed germination due to the embryo
being chemically unready. Such seeds germinate only when they have undergone a process of after
ripening.
Viability - Viability is the potential capacity of a seed to germinate. Seeds of some species retain their
viability for a long period while those of certain other species lose their viability very soon. If the
environmental conditions are not suitable during the short period of viability, such seeds do not
germinate. For example, on the normal conditions Sal seeds remain viable for about a week. So if the
monsoon is delayed, most of the seeds that fall on dry ground die.

16. Size of seed – Very minute seeds are washed away in the rain water, whereas very big seeds do not get
properly covered by soil or humus, and do not germinate.
Germination capacity – Since all the seeds that fall on the ground do not germinate, natural
regeneration is affected by germination capacity of seed, which is defined as the percentage, by
number, of seeds in a given sample that actually germinate, irrespective of time.
Terminalia seeds Teak seeds
Minute seeds

18. Plant percent – All the seedlings that come up after successful germination do not survive
owing to adverse environmental factors. An important indicator of how many seedlings will
eventually establish themselves is the Plant Percent. Plant Percent is defined as percentage
of the number of seeds in a sample that develop into seedlings at the end of the first growing
season.

19. B. External Factors – These are factors of environmentaffecting germination.
Temperature – Heat is necessary for germination. The range of temperature suitable for
germination varies with the species. However, within this range, higher the temperature the
better the germination.
❖ Moisture – A sufficient supply of moisture is essential for development of the embryo.
❖ Air/oxygen – Oxygen is essential for rapid respiration which accompanies the process of
germination. Water-logged or ill-ventilated soil is not suitable for germination.
❖ Light – Most of the species are indifferent to light conditions for germination. However, some
species require light, while some others require shade for germination

20. Rhododendron, Albizzia procera, Cassia fistula.
Species requiring light

21. Species requiring shade
Swietenia macrophylla, Santalum album

22. ❖ Depth of seed covering – If seeds lie on ground with shallow covering of soil, they germinate
early. However, seeds which lie deeper give enhanced germination and establish per cent on
account of adequate supply of moisture.

23. 3. Seedling Establishment
Good germination does not necessarily ensure successful regeneration. A good number of seedlings die due
to frost, drought or other climatic factors. Many suffer casualty owing to biotic factors like weeds, grazing,
burning etc. Thus, establishment of seedlings is what ultimately matters for successful natural regeneration.
Establishment is defined as the development of a new crop, naturally or assisted, to a stage when the
young regeneration, natural or artificial, is considered safe from normal adverse influences such as frost,
drought or weeds, and no longer needs special protection or tending operations other than cleaning,
thinning and pruning. Following factors affect establishment of seedling.
Development of roots – It is essential that the root system develops rapidly and comes in contact with the
deep lying moist soil before drought period sets in. Thus in the species in which root develops fast, the
seedling mortality is less.

24. Soil conditions – For their growth, seedlings require water and food, which they draw from the soil.
Therefore, soil conditions are very crucial for establishment of seedlings.
Soil Moisture – During the growing season the seedlings require adequate moisture for which rapid
development of the root system is essential. Root development primarily depends on carbon
assimilation in leaves which in turn depends on available light and supply of moisture through root
system. Hence if soil moisture becomes deficient, it will hamper root development and thus adversely
affects the process of seedling establishment.

25. Nutrient Conditions - Though plants assimilate carbon and oxygen from the atmosphere, the majority of
macro and micro-nutrients are supplied by ion exchange reactions, mineral weathering or organic matter
decomposition – processes all occurring within soil. Thus deficiency in nutrients in the soil has an adverse
effect on the development of seedlings. Establishment of seedlingForest soils in North Bengal, in general,
do not exhibit any nutrient deficiency. However, forest soils in south- west part of the state are
impoverished in mineral soil and organic matter. s, particularly of exacting and tender species, in such soil
is difficult.
Humus conditions – Presence of thick layer of undecomposed humus indicates deficiency of nutrients in
the soil. It also presents a physical obstruction to the root to penetrate to greater depths to strike fresh
mineral soil before the onset of drought season. Drought mortality is therefore aggravated with a thick
layer of humus.
Soil aeration – A well aerated soil with good texture ensures adequate supply of oxygen and facilitates early
establishment of seedlings.

26. Light Condition – Light is necessary for carbon assimilation by photosynthesis, and root
development. It is the limiting factor in the establishment of seedlings in the humid regions. Light
requirement, however, varies from species to species. Based on their light requirement plants are
classified as Light demanders (requires abundant light for its best development), Shade bearers
(capable of persisiting and developing under shade) and Shade demanders (requires, at least in its
early stage, some shade for normal development).
Other Climatic factors – Extremes of temperature are harmful for establishment of seedlings.
Similarly, moderate rainfall and proper seasonal distribution of rain is beneficial to seedling
establishment.

27. Condition of weed growth – Density of weed growth has a great influence on establishment. The
competing weeds may be grass or shrub or combination of both. A dense growth of grass and when
it forms dense mat-like roots is very harmful to forest crop. Similarly, dense growth of shrubs is
very harmful to the desired species, as these shrubs cut off light.
Grazing, browsing and burning – While light grazing and browsing are not harmful, uncontrolled
grazing and browsing destroy the regeneration. In the same manner, controlled burning does not
cause any harm and rather keeps the growth of shrubs in check. However, uncontrolled burning is
very injurious to establishment.

28. Natural Regeneration by Coppice andRoot Suckers:
Coppice: Stool shoots generally arise from the
adventitious buds formed between the wood and the
bark of the stump and are comparatively short lived
than those produced by dormant buds. These shoots
are called coppice shoots.
Root Suckers: Shoots arises from the roots, may occur
naturally or artificially.

29. Coppicing
 Process of cutting trees down, allowing the stumps to regenerate for a number of years
(usually 7 - 25) and then harvesting the resulting stems.
 It makes use of the natural regeneration properties of many tree specie

30. ClassificationofCoppiceRegeneration:
1) Seedlings Coppice
2) Stool Coppice
Seedlings Coppice Stool Coppice
• Occurs mainly in seedlings/ saplings when cut down
at their base
• Common in natural forest
• Used in vegetative multiplication of potential clones
Ex: Sal and Teak
• Stump after left after felling the tree which is usually
around 15cm height from the ground level
• From this shoots 2-3 leading shoots are allowed to grown
in mature tree
Ex: Eucalyptus and Melia dubia

31. CLASSIFICATIONBASED ONCOPPICINGABILITY
 Strong Coppice
Ex: Eucalyptus, Teak, Shorea, Dalbergia, Albizzia, Cassia, Prosofis, Melia, Morus alba
 Fair Coppice
Ex: Terminalia, Pterocapus, Quercus, Hardwickia, Chloroxylon
 Bad Coppice
Ex: Madhuca indica, Bombax ceiba, Casuarina
 Do Not Coppice
Ex: Pinus, Picea, Abies, Cedrus

32. Pollarding
 Pollarding is a process of cutting back the branches of a tree or shrub.
 It was originally practiced to provide animal fodder or fire wood without killing the tree.

33. Examples of pollarding
Leucaena leucocephala, Gliricidia sepium

34. Root Suckers
 Perennial plants that have adventitious buds on the central and side roots which develop
epigeal shoots, or root sprouts, serving for vegetative reproduction.
 When the roots of the mother plant die, root sprouts on them separate and form new plants
 Ex: Melia dubia, Dalbergia sisoo, Dalbergia latifolia, Bombax ceiba

35. Factors Controlling Natural Regeneration
 Seed Supply – Based on species
 Soil Condition – Nutrients and water
 Competition – Domination of other species
 Predation – Animals and birds
 Natural Hazards – Forest fire, flood and land slides

36. Advantages of Natural regeneration
• Preservation of locally adapted populations
• Preservation of high genetic variability
• Good adaptation to micro-sites
• Undisturbed root development
• Mostly low cost
• Low investment risk

37. Disadvantages
• Inability to change genetic stock
• Irregular regeneration density and tree species composition
• Dependence on fructification and seed production
• Low flexibility
• High management intensity and complexity
• Long risk period